1. Field of the Invention
This invention relates generally to surfactant compositions and, more specifically, to surfactant compositions comprising suspensions of solid surfactants. In particular, this invention relates to suspensions of a solid surfactant, such as an alpha olefin sulfonate, in an organic base fluid, such as diesel or vegetable oil. These suspensions may be optionally combined with additive materials, such as polymers, and/or with aqueous carrier fluids. This invention also relates to various uses for solid surfactant compositions, including as wetting agents, emulsifiers, dispersants, viscosifiers, gelling agents and/or foamers, such as used in drilling, completion and remedial or workover well applications.
2. Description of Related Art
Surfactant-containing solutions are used for many purposes. For example, in oil and gas well applications, these solutions may be employed as part of a carrying fluid, such as a drilling fluid, for supporting and removing solids and liquids from a wellbore. Surfactant-containing solutions may also be utilized in gelled or otherwise thickened fluids for purposes of preventing loss circulation and/or cleaning materials from a wellbore. In addition to intra-wellbore uses, surfactant-containing solutions may also be utilized as part of formation stimulation or hydrocarbon recovery operations. For example, surfactant-containing fluids may be utilized as part of gelled or viscosified liquids used in hydraulic fracturing treatments. These viscosified fluids serve the purpose of initiating a fracture in a formation and of carrying proppant into the formation. Gelled or viscosified surfactant-containing fluids may also be utilized as part of acid jobs or other stimulation treatments. In this capacity, gelled fluids may be used as a diversion agent for diverting acid or other stimulation fluids into less permeable parts of a formation, or those parts of a formation having greater formation damage. In other cases, surfactant-containing fluids may be employed as part of tertiary recovery operations, such as in miscible floods, or to water wet formation surfaces.
In many of the above listed applications, surfactant-containing fluids may also be foamed. In most cases, foams include energizing phase gases such as nitrogen and/or carbon dioxide mixed with water in a suitable surfactant. Foams may be employed in many applications. For example, foams may be employed as part of a stimulation treatment, such as an acid or hydraulic fracture treatment. When employed as part of a stimulation treatment, foams help increase well clean-up efficiency and decrease well clean-up time by expanding to provide energy or pressure to support well clean-up following treatment. Other uses for foams include as a relatively lightweight circulating fluid which may be employed, for example, to clean out wellbores penetrating formations having relatively low bottom hole pressures.
In other cases, surfactants may be employed to assist in the hydration of polymers employed in solutions such as gelled treatment fluids. In such applications, surfactants have been used as dispersant agents in slurries of polymer particles. In this capacity, surfactants help disperse the polymer particles in such a way that the polymers may hydrate, gel and/or increase the viscosity of the fluid. Such surfactant-containing polymer solutions may also be foamed with the addition of a separate foamer prior to addition to an energizing phase such as carbon dioxide, nitrogen or a mixture thereof. Foamers, such as betaines, have typically been employed in water-based foam fracturing applications.
In the past, water-based fracturing foams have typically been made by mixing a dry polymer with water and foamer before addition of an energizing phase. However, it has been found that the use of a dry polymer typically requires batch mixing of the polymer with water to form a polymer solution prior to foaming of the treatment fluid. Disadvantages of this method include increased energy required from surface pumps due to increased viscosity of the polymer solution, and disposal of pre-mixed polymer solution in those cases where a fracture treatment has to be prematurely terminated. To address the problems presented by dry polymer systems, slurry polymer systems have been developed. A typical slurry polymer system includes a slurry of polymer particles in a hydrocarbon fluid base, for example a 50/50 mix of diesel oil and guar or guar-based polymer. By using a hydrocarbon fluid-based polymer slurry, several advantages are realized. First, the polymer may be supplied in liquid form to an aqueous treatment carrier fluid as a job is pumped. This is known as a "continuous mixing" process. Such a process offers the advantage of improved metering and reduced surface pump horsepower. Second, if a fracturing job has to be prematurely discontinued, no unused polymer solution remains which must be disposed of.
Although continuous mix processes utilizing hydrocarbon fluid-based polymer slurries offer many advantages, problems still persist. For example, separate process streams are typically required to supply a number of ingredients, such as surfactants for dispersing and water wetting the polymer particles and a separate roamer. These process streams are in addition to other process streams required for emulsifiers, cross-linkers, etc. With each additional process stream, a continuous mix system becomes increasingly complicated in terms of equipment and operating procedures, especially when delivery rate changes are required. Another problem encountered with continuous mixed hydrocarbon fluid-based polymer systems is that diesel oil and other liquid hydrocarbons used in such systems tend to act as defoamers, making the use of a slurried polymer system with a foamer such as betaine undesirable due to lack of stability of the foam produced.
Multi-component foamer systems have been developed in an attempt to address foam instability problems encountered with the use of hydrocarbon fluid-based polymer slurries. For example, a water-based roamer comprising an alkyl betaine, a liquid alpha-olefin sulfonate, a hydrophilic solvent and water has been developed. Such a foamer is typically added to a fracture gel comprising a polymer/hydrocarbon slurry mixed with brine prior to the addition of an energizing phase. Although such foamer compositions may partially address foam stability problems in the presence of hydrocarbon-based fluids, several disadvantages with such systems remain. For example, such foamers typically comprise several components, thus increasing the compositional complexity of the system. In addition, such foamers typically must be added as a separate process stream to the fracturing gel after addition of an aqueous carrier fluid and after crosslinking, thereby increasing operational complexity. Furthermore, there exists limits to the amount of active foaming components in the foamer composition which may be dispersed in the solvent component of such a foamer system. Consequently, foamer delivery loading is limited by economics. For example, utilizing in excess of 30 gallons per thousand gallons of a liquid betaine/liquid alpha-olefin sulfonate/water-based foamer having a maximum of about 40% concentration of liquid alpha-olefin sulfonate surfactant typically is uneconomical.